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Date: Thu, 28 Jun 2018 11:33:11 -0700 From: Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com> To: Willem de Bruijn <willemdebruijn.kernel@...il.com> Cc: Network Development <netdev@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, jan.altenberg@...utronix.de, Vinicius Gomes <vinicius.gomes@...el.com>, kurt.kanzenbach@...utronix.de, Henrik Austad <henrik@...tad.us>, Richard Cochran <richardcochran@...il.com>, Levi Pearson <levi.pearson@...man.com>, ilias.apalodimas@...aro.org, ivan.khoronzhuk@...aro.org, Miroslav Lichvar <mlichvar@...hat.com>, Willem de Bruijn <willemb@...gle.com>, Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiří Pírko <jiri@...nulli.us>, Richard Cochran <rcochran@...utronix.de> Subject: Re: [PATCH v1 net-next 02/14] net: Add a new socket option for a future transmit time. Hi Willem, On 06/28/2018 07:40 AM, Willem de Bruijn wrote: > On Thu, Jun 28, 2018 at 10:26 AM Willem de Bruijn > <willemdebruijn.kernel@...il.com> wrote: >> >> On Wed, Jun 27, 2018 at 6:08 PM Jesus Sanchez-Palencia >> <jesus.sanchez-palencia@...el.com> wrote: >>> >>> From: Richard Cochran <rcochran@...utronix.de> >>> >>> This patch introduces SO_TXTIME. User space enables this option in >>> order to pass a desired future transmit time in a CMSG when calling >>> sendmsg(2). The argument to this socket option is a 6-bytes long struct >>> defined as: >>> >>> struct sock_txtime { >>> clockid_t clockid; >>> u16 flags; >>> }; >> >> clockid_t is __kernel_clockid_t is int is a variable length field. >> Please use fixed length fields. > > Sorry, int is fine, of course, and clockid_t is used between userspace and > kernel already. Great. So, in addition to the other feedback in sock.c, what I'm thinking here for the v2 is: - move this struct to and the flags definition (as enums) to include/uapi/linux/net_tstamp.h; - keep clockid as a clockid_t and increase flags to u32 since this already takes 8 bytes in total anyway; - reduce sk_clockid and sk_txtime_flags from struct sock from a u16 to a u8 each. Thanks, Jesus > >> Also, as MAX_CLOCKS is 16, only 4 bits are needed. A single u16 >> is probably sufficient as cmsg argument. To future proof, a u32 will >> allow for more >> than 4 flags. But in struct sock, 16 bits should be sufficient to >> encode both clock id >> and flags.
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